1

### JEE Main 2019 (Online) 9th January Evening Slot

In which of the following process, the bond order has increased and paramagnetic character has charged to diamagnetic ?
A
NO $\to$ NO+
B
N2 $\to$ N2+
C
O2 $\to$ O2+
D
O2 $\to$ O22$-$

## Explanation

Molecular orbital configuration of NO (15 electrons) is

${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\sigma _{2p_z^2}}\,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,\pi _{2p_x^1}^ * \, = \,\pi _{2p_y^o}^ *$

$\therefore\,\,\,\,$ Nb = 10

Na = 5

$\therefore\,\,\,\,$ BO = ${1 \over 2}\left[ {10 - 5} \right]$ = 2.5

And in NO one unpaired electron is present , so it is paramagnetic.

Similarly Molecular orbital configuration of NO+ (14 electrons) is

${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\sigma _{2p_z^2}}\,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,$

$\therefore\,\,\,\,$ Nb = 10

Na = 4

$\therefore\,\,\,\,$ BO = ${1 \over 2}\left[ {10 - 4} \right]$ = 3

And in NO+ no unpaired electron is present , so it is diamagnetic.
2

### JEE Main 2019 (Online) 10th January Morning Slot

Two pi and half sigma bonds are present in :
A
O2
B
N$_2^ +$
C
O$_2^ +$
D
N2

## Explanation

Two pi and half sigma bonds are presents in molecule with bond order 2.5.

Moleculer orbital configuration of $N_2^+$ (13 electrons)

= ${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,{\sigma _{2p_z^1}}$

Bond order = ${1 \over 2}\left( {9 - 4} \right)$ = 2.5
3

### JEE Main 2019 (Online) 10th January Morning Slot

The type of hybridisation and number of lone pair (s) of electrons of Xe in XeOF4, respectively, are:
A
sp3d and 2
B
sp3d2 and 2
C
sp3d and 1
D
sp3d2 and 1

## Explanation

H = ${1 \over 2}$ (V + M - c + a)

$\therefore$ H = ${1 \over 2}$(8 + 4) = 6

From structure, it is clear that it has five bond pairs and one lone pair.
4

### JEE Main 2019 (Online) 10th January Evening Slot

The pair that contains two P – H bonds in each of the oxoacids is
A
H3PO2 and H4P2O5
B
H4P2O5 and H4P2O6
C
H4P2O5 and H3PO3
D
H3PO3 and H3PO2